Signal lights contain various kinds of optical systems which collimate a light beam emitted by a light source and then distribute the light in a direction required by international regulations. Among the widely used collimation techniques is collimation by means of a parabolic reflector, collimation by means of a converging lens and collimation by means of a Fresnel type converging lens. Recently, in connection with the use of light-emitting diodes (LEDs), a rotational collimator has also been used for the collimation of light, in which the light beam is collimated by a central entry surface created by a converging lens and outermost entry surfaces working on the principle of total reflection of light. Rotational collimators are part of optical modules which contain, besides the mentioned collimator, also scattering elements necessary for the distribution of the collimated light beam in the directions required by international regulations. Rotational collimators are used in combination with light-emitting diodes, which have a broad radiation characteristic.
In order to achieve the required efficiency needed to achieve the luminous intensity values as required by international regulations, it is necessary for the body of the rotational collimator to have a greater thickness (much greater than 2-3 mm, which is the standard thickness for plastic moldings used in light engineering for automobiles). The greater thickness of the collimator consequently leads to a high price of the molding, a high price of the mold, and also manufacturing problems that are connected with the making of thick-wall plastic moldings. When it is necessary for production reasons to reduce the thickness of the molding, this is achieved by removing part of the collimation surface of the collimator, which necessarily leads to lower efficiency of the optical module.
For a use in signal lights, it is advisable for design and production reasons that the dimension of the collimator is substantially larger in one direction than in another direction perpendicular to it.